Process of carbonizing nickel or other metals



Patented Oct. 4, 1932 UNITED, STATES PATENT OFFICE HOWARD I. ELSEY, OI OAIIONT, PENNSYLVANIA, ASSIGNOR '10 WESTINGHOUSE ELEC- TBIC & HANUI'AGIUBING COMPANY,

A. CORPORATION OF PENNSYLVANIA.

PROCESS OF. CABBONIZING NICKEL OR OTHER METALS Io Drawing.

My invention relates to a process of carbonizing metallic surfaces and more particularly to a process of carbonizing nickel, or other metals, which are used as plates or 5 grids in electron tubes.

An object of my invention is to prov de a process of carbonizing metals, and especlally nickel, in such manner that a uniformly carbonized surface will be produced.

Another object of my invention is to provide a rocess of carbonizin metallic-surfaces w 'ch consists essential y in oxidizing the metallic surface and then subjecting the oxidized metal to the action of a hydrocar bon gas at an elevated tem erature, to produce a uniformly carbonize metal.

In electron tubes having thermionically emissive cathodes particularly cathodes comprising oxides-o the alkaline-earth metals, there 1s a tendenc for the cathode material to volatilize and eposit upon the anodes or other electrodes which are not intended to emit electrons during the operation of the tubes. When electron tubes having a con 25 siderable ower output are emploged, the anodes and grids become heated an the result of such deposits is that they fail to'perform their expected function, but, instead, become emitters of electrons.

In order to prevent the tendency of the ids or plates from emitting electrons, it as been proposed to carbonlze their surfaces. It has been found that the efliciency of anodes and grids carbonized in thissmanner is greatly increased, as a carbonized surface not onl prevents the emission of electrons but a increases the ability of the grids or lates to radiate heat and, consequently, ecreases their operating temperature at a given current. V

In carbonizing nickel, it has formerly been the practice to pack a large number of nickel sheets in a cold electric furnace that could be made gas-tight. A streamof natural as 5 was then passed through the furnace, 's-

Application fled February 4, 1928. semi in. 252,047.

placing the air. During passage of the natural gas the temperature of the furnace was graduall raised until the hydrocarbon gas became ecomposed or until a reaction took place between the hydrocarbon gas and the nickel.

After the nickel was exposed to the action of the carbon resulting from the decomposition of the hydrocarbon gas, or after reaction took place between the nickel and hydrocarbon gas for about an hour, the furnace was then slowl cooled. The carbonized nickel plates mlg t then be removed from the furnace and formed or shaped, as desired, into plates or grids.

' Difiiculty, however, has been experienced in producing an evenly carbonized surface by the method just described. Parts of the nickel surface would be uncoated, or, if the were coated, the carbon could be rubbed 0 ve easily, leaving an undesirable bright surface.

The cracking of a hydrocarbon vapor to yield carbon, as one product, is a reaction which can be accelerated by the presence of a suitable catalytic agent, such as an active nickel surface. I am, therefore, of the opinion that much of the trouble was caused by portions of the nickel varying in catalytic ao- I have made the discovery that the activity of metal surfaces, such as nickel and tungsten and alloys, such as nichrome, may be rendered uniform by previously oxidizing the metals and then exposing the metals to the carbonizing action of a hydrocarbon vapor, referably one that does not contain free ydrogen, at a sufliciently high temperature to decompose the hydrocarbon or to effect a reaction between the hydrocarbon vapors and the oxidized metal. If preferred, the hydrocarbon vapors may be diluted with an inert gas, such as nitrogen, argon, or helium, although this is not essential.

In practicing my invention, the nickel, or other metal, is oxldized in any well-known manner, as by heating the metal and exposing it to a current of air, and is then placed in an air-free furnace through which a h drocarbon gas, preferably free from uncom ined hydrogen such as etroleum gas or casinghead gasoline, which is sometimes sold under the trade name of Bu-tane, may be passed; or, if preferred, the process may be made continuous by oxidizing the metal in one furnace and then placing it in the carbonizing fur- .nace while the gas is flowing.

The furnace is maintained at an elevated temperature, such as from approximately.

r nent form, possibly by the formation of a carbide of the nickel, or by forming a solid solution of carbon in the nickel. After the carbon has been formed upon the nickel sur face, it is heated in vacua to remove any occluded gases or other volatile material. The nickel or other metal may then be formed or shaped into grids or plates, or utilized for other purposes.

By my improved method, the nickel is uniformly carbonized and is much superior for use as grids or plates in electron tubes than electrodes made of metal alone or metal carbonized by previous methods.

The thickness of the layer of carbonized metal which is formed may be controlled by mixing the hydrocarbon vapors with an inert gas, such as nitrogen. When an inert gas is mixed with the hydrocarbon vapors, the carbon does not penetrate so deeply into the metal during the same period 0 time, but a uniformly carbonized surface is produced and the carbon burns in, or alloys with, the metal without obtaining a large excess of carbon, which,-being out of contact with the nickel, cannot enter into solution or reaction with it.

While it cannot be stated definitely that free hydrogen in hydrocarbon gases has a deleterious effect in producing a uniformly carbonized metal, experiments indicate that this is true. I prefer, therefore, to use a hydrocarbon gas free from uncombined hydrogen, although gases containing some free hydro en, such as natural gas, have given very goo results.

While I have described a specific process and product, it will be understood that vari-- ous modifications may be made without departing from the spirit of my invention. For

oxidizin uring the reaction example, other hydrocarbon gases, such as butane, ethylene, or ethane, may be substituted for the casing-head gasoline, and other inert gases, such as argon or helium, may be utilized instead of nitrogen. I desire, therefore, that only such limitations shall be placed upon my invention as are imposed by the prior art or the appended claims.

I claim as my invention:

1. The (process of producing a uniformly carbonize nickel surface which comprises a sheet of nickel and subjecting the oxidized nickel, at an elevated temperature, to the action of a hydrocarbon gas.

2. The process of producing uniformly carbonized nickel which comprises oxidizing the nickel and subjecting the oxidized nickel, at an elevated temperature, to the action of a hydrocarbon compound which is a gas at ordlnary temperatures for a suflicientlength oftime to reduce the nickel oxide and to uniformly carbonize the nickel.

3. The process of producing a uniformly carbonized meta-l substantially free from ox-' ides containing a major proportion of nickel which consists in uniformly oxidizing the metal, placing the uniformly oxidized metal in a furnace, and passing a reducing atmosphere containing a hydrocarbon compound which is a gas at ordinary temperatures through the furnace, the furnace being-maintained at a suflicient temperature and the metal bein exposed-to the gas for a suificient length of time to cause the hydrocarbon gas to reduce the metal oxide and carbonize the reduced metal.

{1. The process of producing uniformly carbonized nickel which comprises oxidizing the nickel, placing the oxidized nickel in a furnace and passing the vapors of casing-head gasoline through the furnace, the furnace being maintained at a sufiicient temperature to cause the vapors of the casing-head gasoline to reduce the nickel oxide and to form a carbonized metal.

5. The process of producing uniformly carbonized nickel which comprises oxidizin the nickel, placing the oxidized nickel in a urnace through which a hydrocarbon gas is flowing, the furnace being maintained as a sufficient temperature to carbonize the metal.

6. The process of producing a uniformly carbonized'alloy containing a major propor tion of nickel which comprises uniformly oxidizing the metal and then exposing the uniformly oxidized metal to a reducing at mosphere containing a hydrocarbon gas for a suflicient length of time to reduce the.

oxide and surface.

7 A process of producing a uniformly carproduce va uniformly carbonized bonized metalfree from oxides for electron,

alloys of nickel containing a ma'or proportion of nickel, and then heating t e metal in a reducing atmosphere containing normally gaseous hydrocarbon to reduce the oxide and carbonize the metal.

8. A process of producing a uniformly carbonized metal free from oxides for electron discharge devices which comprises uniformly oxidizing the surface of metal selected from a group consisting of nickel, tungsten, and alloys of nickel containing a major proportion of nickel, and then heating the metal at temperatures of about 700 C. to 1000 C. in

'a reducing atmosphere containing normally gaseous hydrocarbon to reduce the oxide and carbonize the metal.

In testimony whereof, I have hereunto subscribed my name this first day of February, 1928.

HOWARD M. ELSEY. 

